Fiber

Photo by: Denis Pepin

Fiber, which is found in all plant-based foods, is composed of a group of
compounds that makes up the framework of plants. Although fiber cannot be
digested, it is an essential
nutrient
for good health. The health benefits of a
diet
rich in fiber include lower
cholesterol
and a reduced risk of
heart disease
and certain cancers. Also referred to as roughage, fiber is made up of
many compounds, mostly
carbohydrates
. It can be found in a variety of foods, including wheat, potatoes, and
certain fruits and vegetables. Although the recommended amount of fiber is
20 to 35 grams a day, the average American consumes only 12 to 15 grams on
a daily basis. Asians, on average, consume three times as much fiber as
Americans do.

Types of Fiber

Complex carbohydrates, which are a major source of
energy
for the body, are comprised of two main classes: starch, which is
digestible, and fiber, which is generally not digestible. There are also
two kinds of fiber: insoluble and soluble. Insoluble fiber, found in wheat
bran and some fruits and vegetables, cannot be dissolved in water. This
type of fiber is made up of cellulose and hemicellulose, substances that
offer rigidity to plant material (e.g., the peels and skins of fruits and
vegetables, wood, stems, and the outer coverings of nuts, seeds, and
grains). Insoluble fiber acts as a natural laxative, giving stool the bulk
necessary to move quickly through the
gastrointestinal
tract. In addition to preventing
constipation
and
hemorrhoids
, insoluble fiber may also reduce the risk of colon
cancer
by speeding the passage of food through the digestive tract.

Soluble fiber, found in beans, oats, and some fruits and vegetables, is
fiber that can be dissolved in water. This type of fiber is made up of
pectins, gums, and mucilages. Marie Boyle notes that, because it reduces
the level of cholesterol in the blood, soluble fiber can reduce the risks
of heart and
artery
disease and
atherosclerosis
. When consumed in large amounts, soluble fiber also slows
glucose absorption
from the small intestine, which can be helpful in treating
diabetes
. Finally, a diet high in fiber may also promote weight control and reduce
the risk of developing
obesity
.

How Much Fiber Is Necessary?

According to the American Dietetic Association, the daily goal for fiber
intake is between 20 and 35 grams. However, the average intake in the
United States is only 12 to 15 grams. In contrast, people in China consume
as much as 77 grams of fiber per day. Children also need fiber, although
in different

FIBER CONTENT OF VARIOUS FOODS

Food

Amount

Fiber (g)

SOURCE: Adapted from Edlin et al., 2002.

Whole-wheat bread

1 slice

1.6

Rye bread

1 slice

1.0

White bread

1 slice

0.6

Brown rice (cooked)

½ cup

2.4

White rice (cooked)

½ cup

0.1

Spaghetti (cooked)

½ cup

0.8

Kidney beans (cooked)

½ cup

5.8

Lima beans (cooked)

½ cup

4.9

Potato (baked)

Medium

3.8

Corn

½ cup

3.9

Spinach

½ cup

2.0

Lettuce

½ cup

0.3

Strawberries

¾ cup

2.0

Banana

Medium

2.0

Apple (with skin)

Medium

2.6

Orange

Small

1.2

amounts than adults. For children up to age 18, the recommended daily dose
(in grams) is determined by adding five to a child's age. For
example, a seven-year-old child would need 12 grams of fiber a day.

The recommended daily amount of fiber can be consumed by eating a diet
high in fiber-rich fruits, vegetables, and whole grains. There are several
ways to ensure one consumes enough fiber. First, it is important to read
food labels. Although they do not distinguish between the two types of
fiber, the labels of almost all foods will provide the amount of dietary
fiber in each serving. Raw or slightly cooked vegetables will also provide
an excellent source of fiber. However, overcooking vegetables may reduce
the fiber content. Whole-grain cereals, whole-wheat bread, fresh or dried
fruit, beans, rice, and salad are all good sources of fiber. The table
presents the fiber content of various foods.

Problem with High-Fiber Diets

Including fiber in one's daily diet has definite benefits. However,
although very uncommon, fiber has the potential to cause harm if taken in
excess of 60 or 70 grams daily. "Since fiber carries water out of
the body, taking too much can cause
dehydration
and intestinal discomfort or gas," (Boyle, p. 84). Large amounts
of fiber require a high fluid intake. Therefore, as one increases fiber in
the diet, water intake must also be increased. If one does not consume
enough fluid, then one's stool could become very hard, resulting in
difficult and painful elimination.

Fiber speeds the movement of foods through the digestive system. Since
iron
is mainly absorbed early during digestion, high amounts of fiber may
limit the opportunity for the absorption of iron,
calcium
, and other nutrients. Finally, large amounts of fiber can also cause
deficiencies of nutrients and energy by causing one to feel full before
enough nutrients have been consumed. Children and elderly persons are
especially vulnerable to these concerns, since they eat smaller portion
sizes.

In conclusion, fiber is an important element of the diet and provides
several health benefits. Eating balanced meals containing whole grain and
fresh fruits and vegetables will ensure meeting the proper recommended
allowances.